1. Field of the Invention
The present invention is in the field of recording media for recording information optically as by means of laser rays, and relates more specifically to an erasable recording medium composed of a specific SbSe compound. The invention also has to do with a method of using the recording medium.
2. Description of the Prior Art
Photomagnetic material such as TbFe or GdCo is known as an erasable optical recording material. In an information recording medium using such photomagnetic material, however, the recording information, i.e., the direction of magnetization, must be read using light polarization, making the optical system quite complex. Moreover, since the erasing is performed by an external magnetic field, the apparatus becomes complicated.
There has also been a method proposed where reversible phase transition from an amorphous state to a crystalline state or from the crystalline state to the amorphous state is utilized. The phase transformation from the crystalline state to the amorphous state is performed by rapid heating and rapid cooling so as to record the information. The phase transition from the amorphous state to the crystalline state is performed slowly so as to carry out erasing. Signal reproduction is performed utilizing the variation of reflectivity R and transmitivity .tau. in the amorphous state and the crystalline state. In this method, since the phase transition in the crystalline state to and from the amorphous state is performed by laser light of different quantity and irradiation time so as to perform the recording and erasing, the method is more advantageous in that the optical system is simplified. In such recording method utilizing a phase transition, since the reproduction signal quantity is quite large compared to that produced by photomagnetic material as above described, this method is also advantageous in that recording with a large contrast ratio is possible.
Materials containing Se or low-grade oxides of Te are known for use as such recording materials evidencing phase transition. Among these materials, Sb.sub.2 Se.sub.3 evidences a phase transition from its amorphous state to the crystalline state at about 170.degree. C. and therefore the information recording medium utilizing reversibility in the crystalline to and from the amorphous state of this material is possible. The recording material consisting of Sb.sub.2 Se.sub.3 can be transferred from its amorphous state to its crystalline state by irradiation by a laser beam locally heating this portion to 170.degree. C. or more. Since the transition from the amorphous state to the crystalline state must be performed by holding the temperature to 170.degree. C. or more for a certain period of time, slow heating conditions utilizing the laser ray are necessary. Transition from the amorphous state to the crystalline state is performed by increasing the quantity of irradiation from the laser ray and heating the material to a melting temperature of about 600.degree. C. In this case, rapid cooling is necessary for the transition to the amorphous state. To summarize, the transition from the amorphous state to the crystalline state is performed by slow heating and slow cooling while the transition from the crystalline state to the amorphous state is performed by rapid cooling so as to erase and record the information.
In actual practice, however, the transition from the crystalline state to the amorphous state may not be completely effective in such recording material. This is because even if a portion of the material in the crystalline state is melted by irradiation of the laser ray, it is recrystallized in the cooling process.